Lex与Yacc学习（二）之第一个Lex程序

最新推荐文章于 2021-06-30 16:30:44 发布

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最新推荐文章于 2021-06-30 16:30:44 发布 · 5.5k 阅读

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#lex

用lex识别单词

构建一个识别不同类型英语单词的简单程序。先识别词性（名词，动词等），然后再扩展到处理符合简单英语语法的多个单词的句子。

先列出要识别的一组动词：

is am are were was be being been do does did will would should can could has have had go

识别这些动词的lex程序：

%{
/*
 * 例1-1 单词识别程序 ch1-02.l
 * 识别单词是否是动词
 */
%}
%%
[\t ]+          /*意味着空格的正闭包，忽略空白*/; 
is |
am |
are |
were |
was |
be |
being |
been |
do |
does |
did |
will |
would |
should |
can |
could |
has |
have |
had |
go		{printf("%s: is a verb\n",yytext);}
[a-zA-Z]+		{printf("%s: is not a verb\n",yytext);}

.|\n		{ECHO;/*通常的默认状态：输出匹配模式，复制标点或其它字符*/}
%%

int main()
{
	yyin = fopen("example.txt","r");
		yylex();
	fclose(yyin);
}
int